ovs的revalidator

一般情况下ukey->reval_seq和udpif->reval_seq是一样的，所以在revalidate_ukey函数里need_revalidate是false。

但是如果添加或者删除了openflow rule的规则，udpif->reval_seq会加1。

(gdb) bt
#0  set_tables_version (ofproto_=0x1169f50, version=0xa) at ofproto/ofproto-dpif.c:2017
#1  0x00000000004234b3 in ofproto_bump_tables_version (ofproto=0x1169f50) at ofproto/ofproto.c:473
#2  handle_flow_mod__ (ofproto=ofproto@entry=0x1169f50, fm=fm@entry=0x7fff92440b50, req=req@entry=0x7fff92440b00)
    at ofproto/ofproto.c:6215
#3  0x00000000004235c1 in handle_flow_mod (ofconn=ofconn@entry=0x11f2030, oh=0x11f5060) at ofproto/ofproto.c:6190
#4  0x0000000000423f0c in handle_single_part_openflow (type=OFPTYPE_FLOW_MOD, oh=<optimized out>, ofconn=0x11f2030)
    at ofproto/ofproto.c:8504
#5  handle_openflow (ofconn=0x11f2030, msgs=0x7fff924411a0) at ofproto/ofproto.c:8685
#6  0x0000000000457044 in ofconn_run (handle_openflow=0x423a00 <handle_openflow>, ofconn=0x11f2030)
    at ofproto/connmgr.c:1329
#7  connmgr_run (mgr=0x116a4d0, handle_openflow=handle_openflow@entry=0x423a00 <handle_openflow>)
    at ofproto/connmgr.c:356
#8  0x000000000041def6 in ofproto_run (p=0x1169f50) at ofproto/ofproto.c:1890
#9  0x000000000040b6a4 in bridge_run__ () at vswitchd/bridge.c:3250
#10 0x0000000000411053 in bridge_run () at vswitchd/bridge.c:3309
#11 0x0000000000406d7d in main (argc=<optimized out>, argv=<optimized out>) at vswitchd/ovs-vswitchd.c:127

(gdb) bt
#0  ofproto_flow_mod_start (ofproto=0x1169f50, ofm=0x7fff924409c0) at ofproto/ofproto.c:8020
#1  0x000000000042348d in handle_flow_mod__ (ofproto=ofproto@entry=0x1169f50, fm=fm@entry=0x7fff92440b50, req=req@entry=0x7fff92440b00) at ofproto/ofproto.c:6213
#2  0x00000000004235c1 in handle_flow_mod (ofconn=ofconn@entry=0x11f27c0, oh=0x11f4da0) at ofproto/ofproto.c:6190
#3  0x0000000000423f0c in handle_single_part_openflow (type=OFPTYPE_FLOW_MOD, oh=<optimized out>, ofconn=0x11f27c0) at ofproto/ofproto.c:8504
#4  handle_openflow (ofconn=0x11f27c0, msgs=0x7fff924411a0) at ofproto/ofproto.c:8685
#5  0x0000000000457044 in ofconn_run (handle_openflow=0x423a00 <handle_openflow>, ofconn=0x11f27c0) at ofproto/connmgr.c:1329
#6  connmgr_run (mgr=0x116a4d0, handle_openflow=handle_openflow@entry=0x423a00 <handle_openflow>) at ofproto/connmgr.c:356
#7  0x000000000041def6 in ofproto_run (p=0x1169f50) at ofproto/ofproto.c:1890
#8  0x000000000040b6a4 in bridge_run__ () at vswitchd/bridge.c:3250
#9  0x0000000000411053 in bridge_run () at vswitchd/bridge.c:3309
#10 0x0000000000406d7d in main (argc=<optimized out>, argv=<optimized out>) at vswitchd/ovs-vswitchd.c:127

在type_run()中打印backer->need_revalidate值是REV_FLOW_TABLE。

这时revalidate_ukey()中need_revalidate会是true，should_revalidate()会被掉到。

static bool
should_revalidate(const struct udpif *udpif, uint64_t packets,
                  long long int used)
{
    long long int metric, now, duration;

    if (!used) {
        /* Always revalidate the first time a flow is dumped. */
        return true;
    }

    if (udpif->dump_duration < ofproto_max_revalidator / 2) {
        /* We are likely to handle full revalidation for the flows. */
        return true;
    }

    /* Calculate the mean time between seeing these packets. If this
     * exceeds the threshold, then delete the flow rather than performing
     * costly revalidation for flows that aren't being hit frequently.
     *
     * This is targeted at situations where the dump_duration is high (~1s),
     * and revalidation is triggered by a call to udpif_revalidate(). In
     * these situations, revalidation of all flows causes fluctuations in the
     * flow_limit due to the interaction with the dump_duration and max_idle.
     * This tends to result in deletion of low-throughput flows anyway, so
     * skip the revalidation and just delete those flows. */
    packets = MAX(packets, 1);
    now = MAX(used, time_msec());
    duration = now - used;
    metric = duration / packets;

    if (metric < 1000 / ofproto_min_revalidate_pps) {
        /* The flow is receiving more than min-revalidate-pps, so keep it. */
        return true;
    }

    return false;
}

ofproto_max_revalidator系统默认是500，就是0.5秒。如果dump所有flow的时间大于0.25秒。并且flow的pps很小的话，那么这个flow就很有可能被删掉。并且很有可能所以的flow都会被删掉。在支持offload的老系统上，由于rtnl_lock的原因，这个很有可能被触发。可以通过下面的配置来缓解这个问题：

ovs-vsctl set Open_vSwitch . other_config:max-revalidator=10000